Before he became famous, Albert Einstein remarked that "the foolish faith in authority is the worst enemy of truth". Few wanted to listen to the revolutionary ideas of an unknown patent office clerk who dared to challenge the godlike authority of Sir Isaac Newton. Progressive science is sometimes more conservative than people think.

The story of the peppered moth is a case in point, according to Judith Hooper. Biston betularia is a species of moth familiar to anyone who has studied biology. "You will have glimpsed them in textbook photographs, posed on tree trunks, immortalised and still as figures in a classical frieze." For this otherwise unremarkable moth proved Darwin right - or at least, that's what everyone thought.

The problem with Darwin's theory of evolution by natural selection is that it describes events that occur over thousands of years, and is therefore difficult to prove empirically. But the industrial revolution seemed to offer scientists a perfect example of rapid environmental change, forcing organisms to adapt quickly.

In 1848, a black or melanic form of the peppered moth appeared in Manchester. At the time, 50 tonnes of industrial fallout were deposited annually on each square mile of the city. These pollutants killed the lichens on tree bark, and in 1896 a naturalist linked this with the decline of the lighter form of the moth. In polluted areas the black moths were better camouflaged against the dark tree trunks, and so less likely to be eaten by birds. It was evolution in action, a perfect demonstration of the survival of the fittest. There was just one problem: no one had seen birds eating moths from tree trunks.

In 1953, Bernard Kettlewell, "a loud, eager man" who was invariably dressed in shorts and sandals, began an experiment that would transform the peppered moth into "evolution's number one icon". Camping in woods near Birmingham and sustained by a diet of gin and cigars, Kettlewell set out to prove that birds really did eat more pale moths in darkened, polluted woods. His results were striking. The black moths were twice as likely to survive in the polluted woods as lighter moths. It was one of those rare "eureka" moments: Kettlewell's experiment was what scientists had been waiting for, "living proof of Darwin's theory of natural selection".

In the 1970s, the American lepidopterist Ted Sargent highlighted serious problems with Kettlewell's experiment. But no one wanted to know: his research was ignored by the scientific community and his career stymied. The peppered moth experiment was "sacred"; critics were "demonised", their views dismissed as "heresy". But the evidence grew and in 1998 a prominent biologist, reviewing it in Nature , said his shock at the extent of the doubts was like discovering as a child "that it was my father and not Santa who brought the presents on Christmas eve".

Like any good journalist, Hooper knows a scandal when she sees one. "The unspoken possibility of fraud hangs in the air," she says, noting that Kettlewell's field notes have conveniently disappeared. According to Sargent, one thing is certain: the famous photos of moths on tree trunks were faked, using dead moths and a log. In the wild, peppered moths don't hang around on exposed tree trunks long enough to be eaten, preferring the shady undersides of branches. And then there's the nagging question of whether birds actually eat moths on tree trunks. Several experts claim that it does not happen in the wild. By placing moths on the tree trunks, Kettle-well was effectively laying out a smorgasbord for the watching birds, who soon learned when it was feeding time. This was not natural but unnatural selection.

The question Hooper sets out to answer is why such a shoddy piece of scientific research was so readily accepted by the scientific community and allowed to attain iconic status in evolutionary biology. Her answer: because scientists wanted to believe it. Once it had been cited enough times, it became an irrefutable article of faith. Hooper's meticulous research provides a fascinating insight into the fallibility of scientists - after all, as she points out, they are only human.

To prove the point, she explores the amusing eccentricities of moth men: "we are complete nutcases", says one, with disarming honesty. Surprisingly, she sympathises with Kettlewell, whom she portrays as an outsider in the rarefied atmosphere of Oxford University ("he was not an intellectual"). The villain of the story, in Hooper's view, is his bullying boss at the Oxford School of Ecological Genetics, E B Ford, who exploited Kettlewell's findings and "behaved as if he were auditioning for the Great Book of Eccentric Dons ".

Hooper's absorbing account of a flawed if not fraudulent experiment reveals an all-too-human side to scientists that will annoy professionals and enthral laypeople in equal measure. One thing is clear, though - science is much more than a collection of objective facts and figures. Ambition, jealousy, and megalomania are all part of this complex equation.